1. Field of the Invention
The present invention relates to a head amplifier circuit, and, in particular, to a head amplifier circuit which supplies a writing current to a head which records a digital signal on a recording medium.
2. Description of the Related Art
In a floppy disk drive, a digital signal is converted into a magnetic field through a magnetic head, and is recorded on a floppy disk. At this time, by switching transistors in accordance with the digital signal, the writing current supplied to the magnetic head alternately flows or does not flow. Thereby, the magnetic field generated in the magnetic head is controlled, and writing of information on the floppy disk is performed.
FIG. 1 shows a circuit diagram of one example of a head amplifier circuit in the related art.
The head amplifier circuit 1 in the related art includes a plurality of switching transistor Q1 through Q4. Switching of the switching transistor Q1 through Q4 is performed in accordance with a digital signal, and switching control of a writing current supplied to the magnetic head 2 is performed. The head amplifier circuit 1 further includes an external resistor Ra, connected in series with the magnetic head 2, for controlling the writing current supplied to the magnetic head 2.
The switching transistor Q1 is an NPN transistor, the emitter being grounded, the collector being connected with one end of the magnetic head 2 and connected with the collector of the transistor Q3, and the base being connected with a switching controlling circuit 3. The switching transistor Q1 performs switching in accordance with a switching control signal from the switching control circuit 3, and grounds the end of the magnetic head 2.
The switching transistor Q2 is an NPN transistor, the emitter being grounded, the collector being connected with the other end of the magnetic head 2 through the external resistor Ra, and also, being connected with the collector of the transistor Q4, and the base being connected with the switching controlling circuit 3. The switching transistor Q2 performs switching in accordance with a switching control signal from the switching control circuit 3, and grounds the other end of the magnetic head 2.
The switching transistor Q3 is a PNP transistor, a power source voltage Vcc being applied to the emitter, the collector being connected with one end of the magnetic head 2 and connected with the collector of the transistor Q1, and the base being connected with the switching controlling circuit 3. The switching transistor Q3 performs switching in accordance with a switching control signal from the switching control circuit 3, and supplies the writing current to the one end of the magnetic head 2.
The switching transistor Q4 is a PNP transistor, the power source voltage Vcc being applied to the emitter, the collector being connected with the other end of the magnetic head 2 through the external resistor Ra and connected with the collector of the transistor Q2, and the base being connected with the switching controlling circuit 3. The switching transistor Q4 performs switching in accordance with a switching control signal from the switching control circuit 3, and supplies the writing current to the other end of the magnetic head 2.
The switching control circuit 3 supplies the switching control signals, in accordance with the digital signal which is to be recorded, to the transistors Q1 through Q4, respectively.
FIG. 2 illustrates operations of the example of the head amplifier circuit in the related art. FIG. 2 shows the states of the transistors Q1 through Q4. xe2x80x981xe2x80x99 represents the ON state, and xe2x80x980xe2x80x99 represents xe2x80x98OFFxe2x80x99 state.
When each of the transistors Q1 and Q4 is turned on, and each of the transistors Q2 and Q3 is turned off, shown as xe2x80x98axe2x80x99 in FIG. 2, the terminal Ta of the magnetic head 2 is grounded and the power source voltage Vcc is applied to the terminal Tb. Thereby, the writing current flows through the magnetic head 2 from the terminal Tb to the terminal Ta. At this time, the resistor Ra connected with the magnetic head 2 in series is used for controlling the writing current supplied to the magnetic head 2.
When each of the transistors Q2 and Q3 is turned on, and each of the transistors Q1 and Q4 is turned off, shown as xe2x80x98dxe2x80x99 in FIG. 4, the terminal Tb of the magnetic head 2 is grounded and the power source voltage Vcc is applied to the terminal Ta. Thereby, the writing current flows through the magnetic head 2 from the terminal Ta to the terminal Tb. Also at this time, the resistor Ra connected in series with the magnetic head 2 is used for controlling the writing current supplied to the magnetic head 2.
Further, by turning off any one of the transistor Q1 and Q2, and turning off each of the transistors Q3 and Q4, shown as xe2x80x98cxe2x80x99 and xe2x80x98dxe2x80x99 in FIG. 2, any one of the transistors Q1 and Q2 is grounded, thereby, any one of the terminals Ta and Tb of the magnetic head 2 is grounded. Further, the power source voltage Vcc is not applied to the magnetic head 2. Thus, no writing current flows through the magnetic head 2.
Thus, in the head amplifier circuit in the related art, the switching transistors Q1 through Q4 are used for performing a switching control of connection of the magnetic head 2 with the power source voltage Vcc and the ground, and the resistor Ra connected in series with the magnetic head 2 is used for controlling the writing current.
However, in the head amplifier circuit in the related art, the switching control of supply of the writing current to the magnetic head 2 is performed by the transistors Q1 through Q4. In such an arrangement, there is a possibility that, at the time of switching of the transistors Q1 through Q4, a transitional excessive current flows therethrough.
Further, the writing current supplied to the magnetic head 2 is supplied from the power source voltage Vcc through the transistor Q3 or Q4. Accordingly, the write current depends on the power source voltage Vcc.
The present invention has been devised in consideration of the above-mentioned points. An object of the present invention is to provide a head amplifier circuit which can stably supply the writing current.
A head amplifier circuit, according to the present invention, is provided for supplying a writing current, having a direction in accordance with a recording information, to a head for recording information on a recording medium, and comprises:
reference voltage generating means for generating a reference voltage;
constant current generating means for generating a constant current based on the reference voltage generated by the reference voltage generating means; and
grounding means,
wherein, during one period of time, the constant current generating means supplies the constant current to a first end of the head and the grounding means grounds a second end of the head, and, during another period of time, the constant current generating means supplies the constant current to the second end of the head and the grounding means grounds the first end of the head.
A head amplifier circuit, according to another aspect of the present invention, is provided for supplying a writing current, having a direction in accordance with a recording information, to a head for recording information on a recording medium, and comprises:
a reference current generating circuit for generating a reference current based on a reference voltage;
two constant current generating circuits, each for generating a constant current based on the reference current generated by the reference current generating circuit;
two grounding circuits; and
switching elements,
wherein the switching elements perform switching so that, during one period of time, one of the constant current generating circuits supplies the constant current to a first end of the head and one of the grounding circuits grounds a second end of the head, and, during another period of time, the other one of the constant current generating circuits supplies the constant current to the second end of the head and the other one of the grounding circuits grounds the first end of the head.
In the above-described arrangement, the writing current supplied to the head is generated by either one of the constant current generating circuits each of which generates the constant current based on the reference current generated by the reference current generating circuit. Thereby, it is possible to provide a stable writing circuit.
The head amplifier circuit may further comprise a predetermined voltage supplying circuit, wherein:
the reference current generating circuit comprises a reference voltage generating element for generating the reference voltage, and a constant current circuit for generating the constant current based on the reference voltage generated by the reference voltage generating element;
the switching elements includes two switches, one of the two switches connecting the reference current generating circuit with either one of the two constant current generating circuits, the other one of the two switches causing the predetermined voltage, supplied by the predetermined voltage supplying circuit, to be supplied to either one of the two grounding circuits;
each of the two constant current generating circuits comprises a constant current circuit which generates the constant current when the reference current generating circuit is connected thereto; and
each of the two grounding circuits comprises a switching element which is conductive when the predetermined voltage is supplied thereto from the other one of the two switches.
The reference current generating circuit may include an adjusting element for adjusting the reference current to be supplied to either one of the two constant current generating circuits.
In this arrangement, it is possible to adjust the writing current to be suitable for a particular head.
The adjusting element may comprise an externally connected resistor. In this arrangement, merely by selecting the resistor, it is possible to set the writing current to be the optimum one easily at low cost.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.